1. Technical Field
The invention relates to amplifiers, and in particular to amplifiers that have gain control through a biasing circuit.
2. Related Art
In today""s society, both the presence and use of communication systems are increasing at a rapid pace. Wireless and broadband communication systems and infrastructures continue to grow. This acceleration has created a strong and ever-growing market for electronic equipment that employs more powerful, efficient, and inexpensive communication components.
Electronic equipment such as computers, wireless devices, broadband devices (i.e., standard telephones), radios, televisions and other similar devices may communicate with one another by passing transmission signals through free-space (i.e., air and space) and through guided mediums such as wire, cable, microwave, millimeter wave, sonic, and optical connections. These transmission signals go through a variety of processing during their communication. One process involves amplifying the transmission signals.
Conventionally, a multistage amplifier controlled by a biasing circuit is utilized to linearly increase the power of a transmission signal from its power level at an input of the amplifier to the desired power level at an output of the amplifier. For an input transmission signal having a low power level, each stage of the amplifier generally receives sufficient current from the power supply of the device to operate. As the power level of the input transmission signal increases, each stage of the amplifier may require additional current to operate. The biasing circuit detects the increase in the input transmission signal power level in an amplifier stage and, in response, supplies the additional current to that amplifier stage.
Although this additional current enables the amplifier stage to continue its amplification operation, it also causes the amplifier stage to experience compression. When an amplifier stage experiences compression, its actual output is less than a desired output. For example, if an amplifier stage is to give a gain of 5 decibels (dB) to a transmission signal but only gives 4.5 dB, that amplifier stage can be characterized as experiencing compression. Extreme input transmission signal power levels may actually cause the amplifier stage to shut itself down.
When the power level of the input transmission signal reaches a threshold value, the compression of the amplifier stage reaches a point at which its output is less effective. It is desirable to extend the amplifier gain compression point to a higher output power level.
A system is described to extend an amplifier gain compression point to a higher output power level. Broadly conceptualized, the system may include a multistage amplifier and an enhanced biasing circuit that amplify an input signal. The enhanced biasing circuit may included a voltage follower connected to each stage of the amplifier. Between each voltage follower/amplifier stage connection may be a resistor. Each resistor may increase the power amplification capabilities of an adjacent, upstream amplifier stage in advance of an increase of the input signal so as to extend the gain compression point of the amplifier to an output power level that is higher than conventional amplifiers.
A process performed by the system may include receiving at a driver stage of the amplifier an input signal having a power level that increases over time. The driver stage may amplify this input signal to form an interstage signal that is passed to final stage of the amplifier. The power level of the interstage signal may cause the final stage of the amplifier to draw current from a voltage follower within the biasing circuit. This current may pass through a final stage resistor connected between the voltage follower and the final stage of the amplifier.
Drawing current through the final stage resistor may cause a voltage drop across the final resistor so that the voltage follower output voltage increases. The increase in the voltage follower output voltage, in turn, may increase the voltage over an upstream resistor. The upstream resistor voltage increase may increase the base bias voltage of a driver stage as a function of an increase in the input signal power level and in advance of receiving an increase in the input signal power level. This may increase capabilities of each driver stage so that the overall effect works to extend the amplifier gain compression point to a higher output power level.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.